A US Border vehicle drives along the US and Mexico border fence in Naco, Arizona, in this September 2011 file photo. Arizona’s immigration law threatens to do more than make life unbearably difficult for illegal immigrants, it also threatens Mexico-US relations.

Joshua Lott/Reuters/File

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Washington — Arizona’s tough immigration enforcement law threatens to do more than make life unbearably difficult for illegal immigrants. It also threatens to sour US foreign relations with Mexico and other Latin American nations.

That’s the message in a friend-of-the-court brief submitted in advance of Wednesday’s oral argument at the US Supreme Court over Arizona’s controversial law known as SB 1070.

“SB 1070 poses an imminent threat to Mexico-US bilateral relations,” declares the brief submitted on behalf of Mexico and 16 other countries.

The 45-page friend-of-the-court brief was submitted in support of the Obama administration, which is asking the high court to uphold a federal judge’s decision in 2010 blocking most parts of the Arizona law before it could take effect.

The Mexico brief is interesting, in part, for the information it leaves out.

For example, the brief does not mention that there are an estimated 6.8 million Mexican nationals currently residing in the US without legal authorization. In addition, at least 6 million more Mexicans are legal permanent residents who have not become US citizens.

Last year, Mexicans in the US – both illegal and legal – sent $22.7 billion in family remittances home to Mexico. It is Mexico’s second largest source of foreign revenue after tourism.

Among the 16 countries joining Mexico’s brief are the Central American countries of El Salvador, Guatemala, and Honduras. After Mexico, they are the three largest contributors of undocumented immigrants currently in the US. According to federal estimates, there are 660,000 undocumented immigrants from El Salvador, 520,000 from Guatamala, and 380,000 from Honduras.

Those four countries account for 73 percent of all illegal immigrants currently in the US, according to federal estimates. (That is 8.36 million of an estimated total 11.5 million undocumented immigrants.)

“Mexico asserts its legitimate interest in ensuring that its citizens, regardless of their migratory status, are not deprived of their rights under the US Constitution and international law, or subjected to hostile attitudes or actions by US state actors or the society at large,” New York lawyer Henry Solano wrote in the Mexico brief.

Critics say SB 1070 would encourage illegal racial profiling by police. Supporters say the law can be enforced without attention to race or ethnicity.

Although the Arizona law was blocked, that didn’t stop legislation elsewhere. Five other states enacted similar immigration enforcement laws.

Now the issue is at the Supreme Court where the justices must decide whether Arizona overstepped its authority by enacting a state law designed to enforce federal immigration requirements.

SB 1070 sought to dramatically ramp up enforcement by enlisting state and local officials to check the immigration status of those they suspected were in the US illegally.

The Obama administration took issue with the state-led crackdown, noting that it clashed with President Obama’s priority of seeking to direct federal immigration enforcement at undocumented immigrants who were convicted criminals, while leaving others alone.

In challenging SB 1070, administration lawyers said Arizona was attempting to usurp powers assigned exclusively to the federal government. It is the job of Congress and executive-branch officials to determine who may enter the US and under what conditions they may remain in the country, government lawyers say.

Immigration enforcement, the administration also argues, is intricately connected to the conduct of foreign affairs. The president must be able to speak to the world with a single voice, without interference or conflicting messages from state governments.

That’s where Mexico’s brief comes in. Arizona’s aggressive enforcement posture, the brief says, has already taken a toll on US standing and foreign policy.

In the wake of SB 1070:

• Mexico issued a travel warning about Arizona, advising of “an adverse political atmosphere for migrant communities and for all Mexican visitors.”

• The Mexican Senate put off for a year an emergency management cooperation agreement, while six governors of Mexican border states refused to attend a conference hosted in 2010 by Arizona.

• The legislatures of 14 Mexican states, as well as lawmakers in Brazil, Ecuador, and Peru, expressed opposition to the state law.

• The UN Office of the High Commissioner for Human Rights issued a press release denouncing “a disturbing pattern of legislative activity hostile to ethnic minorities and immigrants.”

In his brief on behalf of Mexico, Mr. Solano said that such foreign-policy complications suggest the Arizona enforcement effort must yield to federal preemption.

“This court has long made clear that state actions that directly interfere with the operation of a federal program are preempted,” he wrote. “SB 1070 directly interferes with federal immigration policy, because it impedes effective and consistent diplomatic relations.”

Most of the post-SB 1070 criticism was directed not at the US government, but at Arizona. Critics of the law organized protests and boycotts against the state and its governor, Jan Brewer (R), not against the US or Mr. Obama.

In an unusual move, the State Department included a paragraph describing the SB 1070 debate in a 2010 report to the UN Human Rights office. The action held Arizona up for international ridicule and condemnation. The UN office received critical remarks from Mexico, Guatemala, Bolivia, and Ecuador, among other nations.

Governor Brewer wrote a blistering letter of protest to Secretary of State Hillary Rodham Clinton. “Apparently, the federal government is trying to make an international human rights case out of SB 1070,” Brewer wrote.

“The idea of our own American government submitting the duly enacted laws of a State of the United States to ‘review’ by the United Nations is internationalism run amok and unconstitutional,” she said.

Brewer urged the State Department to analyze and publish a comparison of how illegal immigrants are treated in Arizona with how they are treated by countries submitting critical comments about SB 1070.

“I am confident that the generous immigration tradition of the United States and Arizona will win in any such comparison,” she said.

It is unclear how Mexico’s brief will be received by the justices. When the case was argued before the Ninth Circuit Court of Appeals, the judges were divided over how much weight to give Mexico’s arguments.

“The record unmistakably demonstrates that SB 1070 has had a deleterious effect on the United States’ foreign relations, which weighs in favor of preemption,” wrote Judge Richard Paez in the appeals-court majority opinion.

The judge said the Arizona law had created “actual foreign policy problems of a magnitude far greater” than those recognized by the Supreme Court in an earlier preemption case.

“These briefs are relevant to our decision-making in this case insofar as they demonstrate the factual effects of Arizona’s law on US foreign affairs, an issue that the Supreme Court has directed us to consider in preemption cases,” Judge Paez wrote.

In a dissent, Judge Carlos Bea said any foreign-relations spillover from the Arizona law would be the result of legal mandates written by Congress, not Arizona.

“A foreign nation may not cause a state law to be preempted simply by complaining about the law’s effects on foreign relations generally,” Judge Bea wrote. “We do not grant other nations’ foreign ministries a ‘heckler’s veto,’ ” he said.

Mexico took exception to Bea’s criticism.

“Mexico is not asserting a ‘heckler’s veto’ over US state or federal laws,” Solano wrote in his Supreme Court brief. The Mexican government acknowledges the sovereign right of countries to decide the policies that will apply within their territory, he said.

“But [Mexico] respectfully asserts its legitimate, substantial and compelling interests to protect the rights of its citizens and support the efforts of the US federal government to ensure that diplomatic relations are not thwarted by the actions of individual states, herein Arizona,” Solano said.

The case is Arizona v. United States (11-182). A decision is expected by late June.